Welcome to the Xtreme Materials Laboratory at the University of California, San Diego

Our CaliBaja Center for Resilient Materials and Systems was inaugurated two years ago and continues to move forward in the development on new materials for extreme environments. Additional information can be found at:

We have designed and studied the response of amorphous steels to shock wave compression. Experiments have yielded results indicating a Hugoniot Elastic Limit (HEL) close to 12 GPa, which is higher than elastic limits for any metallic glass reported. The materials have received very significant media attention and the press release from UC San Diego is found here.

We present a cathodoluminescence study of the spatial distribution of Eu2+ and Eu3+ dopants in hydroxyapatite powders. The results demonstrate that the distribution of europium ions in the hydroxyapatite lattice depends on their valence state. Monochromatic cathodoluminescence images from prismatic powders show that while the Eu2+ is distributed homogeneously in the entire powder volume, the Eu3+ is present mainly at the powder edges. The luminescence spectrum of the Eu2+ ions displayed a wide and strong blue emission centered at 420 nm, while the luminescence spectrum of the Eu3+ ions displayed several orange-red emissions covering the range from 575 to 725 nm. These emissions correspond to transitions between levels 4f65d1 - 4f7 (8S7/2) of the Eu2+ ions and 5D0 - 7FJ levels of the Eu3+ ions. Micro Raman measurements reveal that europium doping generates two phonon signals with frequencies of 555 and 660 cm-1, both of which have not been reported earlier. The powders were synthesized by the combustion synthesis method, maintaining constant the concentration of the europium salt used, and varying the pH of the precursor solutions to modify the concentration ratio of Eu2+ with respect to Eu3+. X-ray photoelectron spectroscopy measurements were used to determine values of 0.32 and 0.55 for the ratio Eu2+/Eu3+ in samples synthesized at pH values of 6 and 4, respectively. Thermal treatments of the samples, at 873 K in an oxygen atmosphere, resulted in a strong quenching of the Eu2+ luminescence due to oxidation of the Eu2+ ions into Eu3+, as well as probable elimination of calcium vacancy defects by annealing.

A detailed analysis of the microstructure and pore evolution of TaC was completed and three pore-forming mechanisms have been discovered: (i) evolution of oxygen impurity; (ii) evolution of excess carbon, and (iii) incongruent sublimation of TaC. The evolution of oxygen impurities is the predominant mechanism and is thought to be the consequence of the high level of oxygen impurity typical of nanopowders; however, all mechanisms must be considered in order to completely eliminate porosity. We propose that the latter two mechanisms can be facilitated by local hot spots and discuss a possible source. The sphere-like morphology and distribution of isolated pores at grain interfaces, edges, and corners indicate a high surface energy of the pores with respect to the grain boundary energy so that the pores become trapped in the microstructure. The root cause of the three mechanisms indicates that a limiting sintering temperature (2173 K) and carefully controlled chemistry are essential for producing TaC without trapped porosity. We propose that these three mechanisms define the sintering behavior of bulk TaC and that similar mechanisms need to be considered for the sintering of other carbide ceramics.

Transition-metal oxides such as WO3 are of interest because of their photochromic, electrochromic, and photocatatytic properties. These applications require a detailed understanding of the morphology, particle size, and other material characteristics for effective utilization and implementation. We present a correlation between powder particle size, determined from dynamic light scattering, and the bonding characteristics of WO3 powders, showing that the W–O–W / W═O integrated intensity ratio is directly related to the particle size of our powders. This correlation can serve as a complementary technique to gauge particle size as well as crystallinity in WO3 powders.

We continue to explore the devitrification behavior of iron-based amorphous alloys. We have developed a relationship between crystallite size, time, and temperature of sintering, and propose a time-temperature-crystallinity diagram that is useful for predictive purposes and for guidance on the spark plasma sintering of amorphous metals. In addition, we propose that dynamic pressing can enhance formability, and demonstrate that density of an iron-based marginal glass forming alloy (Fe49.7Cr17.1Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) can be enhanced by coupling loading rate to fast heating rate during spark plasma sintering. The combination of coupled loading/fast heating and the time-temperature-crystallinity diagram define the processing requirements for obtaining a dense X-ray amorphous structure and can also be used to design a wide variety of dense in situ composites. Finally, we demonstrate that the design approach also applies to ex situ composites by adding microcrystalline W or Ta, enabling systematic control of atomic-, nano-, and micro-structure. This multi-scale structure control of bulk metallic glass composites has implications for developing a fundamental understanding of structure-property relationships. We expect this general approach will be applicable to other bulk metallic glass composites, and especially beneficial for marginal glass formers that are otherwise difficult to process.

We have analyzed the fundamental behavior of reverse micellar systems with respect to a variety of salts additions, including NH4OH, ZrOCl2, and Al(NO3)3. We have demonstrated that the reverse micelle size decreases with increasing salt additions until one reaches a critical concentration, which characterizes the onset of system destabilization. The concept of an electrical double layer, as it applies to reverse micelles, is considered for explaining features of destabilization, including the initial decrease in reverse micelle size, the destabilization concentration, and the effect of cation valence. We propose that the reduction in size prior to instability is caused by compression of the reverse micelle electrical double layer, as higher concentrations of salts are present. These effects have important implications for the preparation of nanopowders by reverse micelle synthesis.

We have worked on a combustion synthesis methodology for the synthesis of non-oxide ceramics. Combustion synthesis is a technique that has been extremely successful for the preparation of oxides, but until now had never been shown to be effective for borides. Work in our laboratory focuses on the preparation of nanocubes of rare-earth hexaborides, including LaB6, SmB6, EuB6, and YbB6. The figure below shows the hexaborides that can be produced by this technique, as well as those that cannot be prepared by this technique. The resulting powders are well-defined nanocubes.

We have pursued efforts to understand the effects of powder agglomeration and thermal conductivity in copper-based nanofluids. We have proposed a correlation between an experimentally determined particle size distribution from dynamic light scattering and the thermal conductivity enhancement of the nanofluid with respect to nanopowder loading. Synthesis of the copper powders was achieved using polyvinylpyrrolidone, oleic acid, and cetyl trimethylammonium bromide (CTAB). The CTAB-prepared powders exhibited the best dispersion characteristics, forming particles of approximately 80 nm in the presence of SDBS. This study is the first to decouple the effect of a carefully characterized particle size distribution versus crystallite size on the thermal conductivity enhancement of a nanofluid.

We have explored the use of a solvothermal process for the synthesis of tantalum carbide and other non-oxide ceramics. The particle size distributions (on the left) from dynamic light scattering show particles that are ~100 nm on average. For a material such as TaC, these particle sizes are some of the smallest that can be found. The crystallite size of the powders is 25 nm, showing that the powders are agglomerated to some extent, but the level of agglomeration is very minor. The technique used for the preparation of the TaC can also be applied for HfC, BN, TiN, among others.

We have used molecular dynamics simulations and dynamic light scattering measurements to analyze the size of reverse micellar structures in the AOT-water-isooctane system at different water-to-surfactant ratios at ambient temperature and pressure. The combination of molecular dynamics and dynamic light scattering allows a better interpretation of the experimental results, in particular for conditions where the structures are nonspherical, commonly observed at lower water-to-surfactant ratios. We have also analyzed the effect of zirconyl chloride on the micellar size distributions in this system.

Reverse micellar systems have a wide range of applications, from protein extraction to synthesis of nanoparticles. They also have an important role during transport processes in biological systems.

NEWS

October 2018

Prof. Graeve was featured in the San Diego Union-Tribune as part of the "Our Immigrant Story". The article can be found here.

September 2018

Graeve was featured in the Tam on STEAM column of the Sally Ride Science @ UC San Diego. The article can be found here.

August 2018

ENLACE 2018 ended! The program this summer consisted of 104 students. A KPBS article on the program can be found here. UC San Diego also featured the program in the News Center.

Our Cross-border Innovaton Summit was a great success! We signed ten collaboration agreements with institutions in Baja California, officially establishing the CaliBaja Education Consortium, and students were able to listed to talks from excellent faculty. Additional information on this event can be found at:

We successfully finished our first ever Summer Engineering Institute (below with keynote speaker, Jose Delgado, at the closing event). This program enhances our efforts in the retention of students in engineering. A press release of the Institute can be found here. The event was also highlighted in Chancellor Khosla's blog.

Credit: Erik Jepsen/UC San Diego Publications

August 2016

Prof. Graeve was inducted into the Mexican Academy of Engineering on August 25 at the beautiful Palacio de Minerias in Mexico City.

Our ENLACE 2016 summer high school program ended on Friday, August 5, after seven intense weeks of participating in research activities at UC San Diego. This year we had the participation of 70 students.

Prof. Graeve presented a series of seminars on materials processing at the Universidad Autonoma de Baja California and the Universidad Tecnologica de Tijuana on April 20.

October 2015

At the PCI Gala Banquet representing UCSD together with Michelle Camacho (ACE Fellow).

September 2015

Prof. Graeve was awarded the Distinguished Alumna award by Southwestern College at the "In a Word" banquet on Thursday, September 17.

September 2015

Prof. Graeve was a featured guest at Bordear el Desierto on Friday, September 4. This is a Mexican national public radio program (on Fusion IMER 102.5 FM) that presents and discusses border issues, as connected to human rights. A full recording of the program can be found here.

May 2015

At the School of Global Policy and Strategy 2015 Launch with Senator Denise Ducheny and Consul Remedios Gomez Arnau.

Ms. Brianna Fernandez, a student in our Tijuana high school summer program during 2013 just received the Kyoto Prize Scholarship. Congratulations to Brianna!

Olivia Graeve, Brianna Fernandez, and Rommie Amaro at the Kyoto Prize Dinner that took place in San Diego on March 17, 2014.

November 2013

Prof. Graeve has just completed her term as President of the National Institute of Ceramic Engineers (NICE). She handed responsabilities to Dr. Kristen Brosnan, the newly installed President of NICE, during a ceremony at MS&T 2013.

Kristen Brosnan and Olivia Graeve at MS&T 2013 during the annual meeting of the National Institute of Ceramic Engineers.

October 2013

Prof. Graeve was a panelist for the "Using Contributions to Diversity in Hiring and Selection" panel at the University of California ADVANCE PAID Roundtable, which took place on Friday, October 25, on the UC San Diego campus. Her presentation can be found here and a final report on this workshop is available here.

Video of panel (available from UC TV).

August 2013

The summer research program for Tijuana, Mexico, high school students came to a very successful end. The five girls from "La Paz" high school were involved in research as diverse as the development of new materials for batteries, characterization of colloidal systems, and molecular dynamics simulations of proteins. All five students presented their research to an audience of approximately 70 guests on the 9th of August.